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LAN Design: Switching Domains and Alleviating Network Congestion

This chapter discusses LAN design principles, including switching domains and how switches help alleviate network congestion. It also explores the growing complexity of converged networks and the benefits of Cisco Borderless Networks.

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LAN Design: Switching Domains and Alleviating Network Congestion

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  1. Chapter 4: Switched Networks

  2. 4.1 LAN Design

  3. Switching DomainsBroadcast Domains A broadcast domain is the extent of the network where a broadcast frame can be heard. • Switches forward broadcast frames to all ports; therefore, switches do not break broadcast domains. • All ports of a switch, with its default configuration, belong to the same broadcast domain. • If two or more switches are connected, broadcasts are forwarded to all ports of all switches, except for the port that originally received the broadcast.

  4. Switching DomainsAlleviating Network Congestion Switches help alleviate network congestion by: • Facilitating the segmentation of a LAN into separate collision domains. • Providing full-duplex communication between devices. • Taking advantage of their high-port density. • Buffering large frames. • Employing high-speed ports. • Taking advantage of their fast internal switching process. • Having a low, per-port cost.

  5. Converged NetworksGrowing Complexity of Networks • Our digital world is changing. • Information must be accessed from anywhere in the world. • Voice, Video, wireless, wired data, critical systems (servers) all ride on the same physical network gear (infrastructure).

  6. Converged NetworksElements of a Converged Network • To support collaboration, networks employ converged solutions. • Data services include voice systems, IP phones, voice gateways, video support, and video conferencing. • Call control, voice messaging, mobility, and automated attendant are also common features. • Multiple types of traffic; only one network to manage. • Substantial savings over installation and management of separate voice, video, and data networks. • Integrates IT management.

  7. Converged NetworksCisco Borderless Networks • What is a network architecture that allows organizations to connect anyone, anywhere, anytime, and on any device securely, reliably, and seamlessly?

  8. Converged NetworksHierarchy in the Borderless Switched Network Borderless switched network design guidelines are built upon the following principles: • Hierarchical • Modularity • Resiliency • Flexibility

  9. Converged NetworksAccess, Distribution, and Core Layers

  10. Switched NetworksRole of Switched Networks • Switching technologies are crucial to network design. • Switching allows traffic to be sent only where it is needed in most cases, using fast methods. • A switched LAN: • Allows more flexibility • Allows more traffic management • Supports quality of service, additional security, wireless, IP telephony, and mobility services

  11. Switched NetworksForm Factors Fixed Configuration Switches

  12. Switched NetworksForm Factors Modular Platforms

  13. Switched NetworksForm Factors What are Stackable Switches?

  14. 4.2 The Switched Environment

  15. Frame ForwardingSwitching as a General Concept in Networking • A switch makes a decision based on ingress and a destination port. • A LAN switch keeps a table that it uses to determine how to forward traffic through the switch, aka the CAM table. Content Addressable Memory. • Cisco LAN switches forward Ethernet frames based on the destination MAC address of the frames.

  16. Frame ForwardingDynamically Populating a Switch MAC Table • A switch must first learn which devices exist on each port before it can transmit a frame. • As a switch learns the relationship of ports to devices, it builds a table called a MAC address or content addressable memory (CAM) table. • CAM is a special type of memory used in high-speed searching applications. • The information in the MAC address table is used to send frames. • When a switch receives an incoming frame with a MAC address that is not found in the CAM table, it floods it to all ports, except the one that received the frame.

  17. Frame ForwardingSwitch Forwarding Methods

  18. Frame ForwardingStore-and-Forward Switching • Allows the switch to: • Check for errors (via FCS check) • Perform automatic buffering • Slower forwarding process

  19. Frame ForwardingCut-Through Switching • Allows the switch to start forwarding in about 10ms • No FCS check • No automatic buffering

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